This invention relates to a fuel metering unit for a gas turbine engine that employs a shut-off valve and an ecology function.
Fuel metering units are used to provide a desired quantity of fuel to, for example, a gas turbine engine used in aircraft. Aircraft fuel systems must meet numerous requirements. For example, the flow of fuel must be precisely modulated to provide the turbine engine's fuel needs. The flow of fuel must be shut-off without any leakage when fuel is no longer needed at the turbine engine. Typically, a shut-off valve is provided that is open and closed using a solenoid. The solenoid is controlled by a controller that commands the shut-off valve based upon numerous sensors. Failure of any component used to control the shut-off valve can result in a malfunction and fuel leak.
It is also desirable to drain fuel during shut down from a manifold with nozzles that is used provide fuel to the turbine engine's combustor. The fuel is drained from the manifold and nozzles to avoid environmental impact, fire risk and coking of the nozzles. The fuel is returned to the tank, and combustion products from the nozzles cannot be introduced into the fuel, which could cause contamination and corrosion. To this end, an ecology valve is used to provide the flow of fuel back to the fuel tank. The ecology valve typically includes a valve actuated by a solenoid or other actuator. Sensors are monitored by the controller and are used to open and close the ecology valve.
The valves within the fuel metering unit must withstand the pressure from the aircraft fuel supply when turbine engine is shut down. Moreover, a failure of any of the fuel system components cannot lead to an incorrect fuel flow to the turbine engine. The solenoid operated shut-off and ecology valves and associated sensors in the prior art are complex, and designing a system to avoid an adverse impact from their failure typically leads to increased cost and complexity. What is needed is a simplified and reliable fuel system for providing fuel to a gas turbine engine and aircraft.